The digital image sensor, such as a charged coupled device (CCD), of a digital camera has a plurality of photo-sites arranged in a colored filtered array or pattern, such as a RGB Bayer pattern. In the RGB Bayer pattern, each photo-site is filtered so that it is receptive to either: red, green, blue, or some variation thereof. The type of colored filter array and digital imaging sensor varies typically based on the manufacture of the digital camera. For example, some color filtered arrays use a pattern of yellow, cyan, green, and magenta. Typically, the digital camera has an image pipeline that performs a demosaicing or de-Bayering process on the image, lens correction, and an RGB contrast and saturation boost. Finally, a noise reduction process may be performed, and the data is encoded into the YCbCr family of color spaces or other format suitable for displaying and viewing.
Various considerations must be addressed when processing a digital image obtained with a digital camera, digital video camera, or other imaging device. One consideration involves preserving the spatial quality and the detail of the digital image, while another consideration involves sufficiently representing the color of the digital image. In many ways, these two considerations are interrelated.
Another well-known “boosting” technique used to render digital images more visually appealing is the use of tone-mapping curves. Tone mapping is a technique used in image processing and computer graphics to map one set of colors or image characteristics to another set of values, often to approximate the appearance of high dynamic range images in media with a more limited dynamic range. However, with conventional tone mapping techniques, one has to find a single tone curve that matches all possible scenes or has to get user input to select which tone curve is appropriate. Further, some conventional tone mapping techniques use symmetrical tone curves. These symmetrical tone curves would boost (or decrease) two data points equidistant from a mean input value by the same amount, regardless of whether the data point represented a lower-than-mean value or a higher-than-mean value. Prior art boosting techniques such as those described above could result in visually unappealing photos in certain scenes or light levels.